The present invention pertains to surface-modified colloidal abrasive polishing compositions and associated methods of using these compositions, particularly for chemical mechanical planarization (CMP, also known as chemical mechanical polishing).
CMP is now widely known to those skilled in the art and has been described in numerous patents and open literature publications. Some introductory references on CMP are as follows: “Polishing Surfaces for Integrated Circuits”, by B. L. Mueller and J. S. Steckenrider, Chemtech, February, 1998, pp. 38–46; and H. Landis et al., Thin Solids Films, 220 (1992), p. 1.
In a typical CMP process, a substrate (e.g., a wafer) is placed in contact with a rotating polishing pad attached to a platen. A CMP slurry, typically an abrasive and chemically reactive mixture, is supplied to the pad during CMP processing of the substrate. During the CMP process, the pad (fixed to the platen) and substrate are rotated while a wafer carrier system or polishing head applies pressure (downward force) against the substrate. The slurry accomplishes the planarization (polishing) process by chemically and mechanically interacting with the substrate film being planarized due to the effect of the rotational movement of the pad relative to the substrate. Polishing is continued in this manner until the desired film on the substrate is removed with the usual objective being to effectively planarize the substrate.
CMP processing is often employed in semiconductor manufacturing to remove excess metal at different stages. Typically, metal CMP slurries contain an abrasive, such as silica or alumina, suspended in an oxidizing, aqueous medium.
Surface modification of the abrasive is known. Colloidal silica, for example, has been modified with various metallic compounds as disclosed in U.S. Pat. Nos. 3,252,917, 3,620,978 and 3,745,126; EP Patent Publication 1 000 995 A1; and also in the book entitled “The Chemistry of Silica”, R. K. Iler, Wiley Interscience (1979), pages 410–411.
Colloidal silica has been stabilized with boric acid as disclosed in U.S. Pat. No. 2,630,410. See also co-pending U.S. patent application Ser. No. 10/245,440, filed Sep. 17, 2002, which discloses a surface-modified colloidal abrasive (e.g., ceria or silica) that has been modified with boron-containing compound(s).
In order to achieve fast tungsten or copper removal rates, oxidants and co-oxidants have been reported in the patent literature. For tungsten CMP, oxidants such as periodic acid, potassium iodate, ferric nitrate, and hydrogen peroxide (H2O2) are commonly used. For copper CMP, H2O2 is a commonly used oxidant. Of all the oxidants in commercial use, H2O2 is low cost, and it is benign from the standpoint of product stewardship, as the byproduct is water. However H2O2 is a poor oxidant for tungsten as it reacts very slowly, so an additive that can catalyze the reaction between tungsten and H2O2 during CMP is highly desirable. See, e.g., U.S. Pat. No. 5,958,288 to Mueller et al., which describes the use of soluble metal co-catalysts for activating H2O2 for the planarization of tungsten. See also SU 1629353, which discloses a composition and method for CMP of aluminum alloys, wherein soluble iron (iron chloride) is used to activate sodium perborate in the presence of diethyldithiophosphoric acid and ninhydrin. SU 120891 discloses a composition and method for CMP of stainless steel, wherein the composition comprises nitric acid, hydrochloric acid, water, oxalic acid, silicon dioxide powder, and acid potassium fluoride as a halogen ion source.
While the use of soluble metal co-catalysts increases the speed at which H2O2 reacts with tungsten, they also require CMP slurries with large concentrations of dissolved, ionic metallic components. As a result, the polished substrates can become contaminated by the adsorption of charged species from the metal co-catalysts. These species can migrate and change the electrical properties of the devices, for example at gates and contacts, and change the effective dielectric properties of dielectric layers. These changes may reduce the reliability of the integrated circuits with time. Therefore, it is desirable to expose the wafer only to high purity chemicals with very low concentrations of mobile metallic ions.
Accordingly, it is desired to provide a polishing composition that does not contain large concentrations of dissolved metal ions. It is further desired to provide a polishing composition particularly suitable for conducting metal CMP, such as copper CMP and tungsten CMP, which composition contains an additive to catalyze the reaction between metal substrate and H2O2, but does not contain large concentrations of dissolved metal ions.
All references cited herein are incorporated herein by reference in their entireties.